Field of the Invention
This invention relates generally to an apparatus and method for removing metal chloride condensate, such as condensable aluminum chloride vapor, that is being exhausted through the exhaust lines of a dry metal etching system in order to control the build-up of such condensate and prevent the eventual clogging of vacuum pump lines, valves, and other components downstream from the etching system. The invention comprises an apparatus that may be automatically translated through the interior of such lines to remove accumulated condensate. Further, the apparatus may be configured so as to sense the accumulation of the condensate and automatically actuate the apparatus to remove the accumulated condensate.
In a typical aluminum etching process for producing components for semiconductor devices, a silicon wafer or other substrate having a film of aluminum on its top surface is positioned in a reaction chamber, and the chamber is evacuated to a vacuum of about 10 millitorr using various well-known vacuum pumping mechanisms, such as for example, a combination of a turbo pump and a mechanical vacuum pump which are connected to the reaction chamber via a foreline. A photoresist that defines the desired metallization pattern is placed on the aluminum surface to protect part of the aluminum film. The exposed part of the aluminum film that is not protected by the photoresist is then removed by etching through the introduction of a low pressure, reactive, chlorine-containing gas such as chlorine (Cl2) or boron trichloride (BCl3). Typically, the etching reaction is plasma-enhanced, where the reaction between the chlorine-containing gas and the aluminum film is enhanced by applying radio frequency (RF) power to the reaction chamber to create a plasma comprising the atomic constituents of the reactive gas in high energy states in the chamber. The generation of the plasma also causes the reaction chamber to heat up, typically to a temperature of 100 to 150xc2x0 C. The plasma-assisted reaction between the aluminum film and the chlorine-containing reaction gas etches aluminum from the exposed areas of the aluminum film, resulting in the formation of a condensable aluminum chloride vapor (AlCl3) reaction byproducts. The reaction chamber effluent, which contains the condensable aluminum chloride vapor in addition to excess chlorine-containing reaction species, is removed from the reaction chamber by the application of a vacuum using well-known vacuum pumping techniques. An exhaust line 2 leading from the vacuum pump then directs the effluent 4 to a scrubber 6, where the condensable aluminum chloride vapor and any excess chlorinated reaction gases are collected as shown in FIG. 1. A wet scrubber employing water is often employed to combine the gaseous aluminum chloride vapor and excess chlorinated reaction gas effluent with water to produce various aqueous species that can be treated using well-known waste treatment methods.
The condensable chloride byproduct in the conventional aluminum etching systems described above cause problems downstream from the reaction chamber, because they condense, solidify, and deposit upon contact with cool surfaces, such as the cooler interior surfaces of the vacuum forelines and exhaust lines that are used to convey the effluent gas away from the reaction chambers, as well as in other components of the vacuum conduit system of the etching system. As shown in FIG. 2, a buildup of solid aluminum chloride 8 downstream from the etching chamber can partially or even entirely clog the pipes.
As shown in FIG. 3, it is well known to heat the vacuum conduit 2 used to exhaust the reaction chamber using a heater, such as heating tape 10, to prevent the condensation of the gaseous species 4 created in the etching reaction. For example, typically, the vacuum in the foreline of an aluminum etching system is approximately 500 millitorr, and consequently it is necessary to heat the vacuum conduit to a temperature of about 70xc2x0 C. in order to keep condensable species, such as aluminum chloride vapor, in the vapor phase so that they can be removed from the chamber and the foreline by the applied vacuum. However, the pressure in the exhaust line between the pump and the scrubber is typically much higher, for example 760 torr, and therefore it is necessary to heat the exhaust lines to even higher temperatures, typically around 105xc2x0 C., to keep the condensable aluminum chloride vapor in the vapor phase as the effluent flows through the exhaust lines. In addition, in the region adjacent to the scrubber 6, there is also typically a partial pressure of water vapor available for the etching reaction by-products to react with, yielding additional condensable reaction products that can condense and clog the exhaust lines. If either the foreline, the exhaust line, or both are not maintained at the proper temperature, the condensable species 8 will cool, condense, and solidify, and species such as condensed aluminum chloride solids will build up along the interior surfaces of the vacuum conduit system, resulting in the diminished function or clogging of the vacuum source.
Additional measures used to control the buildup of solid aluminum chloride in vacuum forelines and exhaust lines in vacuum systems of etching systems are known, including various forms of traps. However, since it is difficult to maintain all parts of an entire vacuum conduit system of an aluminum etching system at the proper temperature to ensure that condensation does not occur, or to efficiently trap condensable etching by-products with conventional traps, the buildup of solid aluminum chloride will inevitably occur throughout the vacuum conduit system of an aluminum etch system, particularly near the interface with the wet scrubber. Consequently, in spite of the heating jackets, heating tape, and various types of traps already available, there is still a need for an improved apparatus and method to prevent the accumulation of condensable species.
The present invention is an apparatus for removing deposits from a pipe, comprising: a reversible drive means; a drive screw having a longitudinal axis, said drive screw located adjacent to an exterior surface of the pipe such that a longitudinal axis of the pipe and the longitudinal axis of the drive screw are substantially parallel, said drive screw rotatably attached to said drive means; a ball nut that is translatably affixed to said drive screw, said ball nut having an anti-rotation means for limiting the rotation of the ball nut in conjunction with rotation of the ball screw; a first tube that is fixedly attached to said ball nut and capable of being magnetized, said first tube adapted to be translated over an outer surface of the pipe and having a longitudinal axis that is substantially parallel to the longitudinal axis of the pipe; a second tube that is adapted to be translatably positioned on the interior of the pipe and capable of being magnetized having an outer diameter adapted to permit said second tube to be positioned inside the pipe such that an exterior surface of the second tube is adjacent an interior surface of the pipe, and having a longitudinal axis that is substantially parallel to the longitudinal axis of the pipe. Preferably, the drive means is an electric motor. The apparatus may also include a controller, such as a microcomputer controller, for controlling the motor that is in signal communication with said electric motor; a pressure sensor for sensing the pressure in the pipe that is in signal communication with the controller; and at least two position sensors that are adapted to sense the position of the apparatus. The apparatus can sense an increase in the ambient pressure within the pipe and through the controller energize the motor to rotate the ball screw, thereby translating the ball nut and the first tube along the length of the ball screw. The second tube is magnetically attracted to the first tube and is thereby translated inside the pipe in conjunction with the translation of the first tube. The position sensors are used to detect the position of the apparatus through the controller. These position signals may be used to determine the travel limits of the apparatus.
The apparatus described above may be controlled using the method of sensing the ambient pressure within the pipe; communicating a signal indicative of the ambient pressure within the pipe to the controller; monitoring the signal indicative of the ambient pressure within the pipe using the controller so as to identify changes in the ambient pressure; communicating a drive signal from the controller to the drive means in response to a change in the ambient pressure, so as to cause the apparatus to be translated along the pipe; sensing one of the first or second positions using respectively one of the first or second position sensors; communicating a signal indicative of the position of the apparatus to the controller; and communicating a drive signal from the controller to the drive means in response to the signal from the position sensor. The drive signal may be a signal to stop the motor or to cause the motor direction to be reversed. In the case where the motor is reversed, the method may further comprise sensing the other of the first or second positions using respectively the other of the first or second position sensors; communicating a signal indicative of the position of the second tube to the controller; and communicating a drive signal from the controller to the drive means in response to the signal from the position sensor. The steps of the method may be repeated a number of times or cycles until the pressure sensor detects that the pressure in the pipe has returned to a desired ambient pressure and the position sensors indicate that the apparatus is in a desired stop position.